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Quantification of Feedstocks for

Anaerobic Digestion Group Report A Northern Ireland Case Study

Appendix 3.1, Biogas Action Plan for Northern Ireland

Appendix 3.1. Feedstocks for AD Page 2 of 26

Quantification of Feedstocks for Anaerobic Digestion Group Report

This report was prepared as a support for the Biogas Research Action Plan for Northern Ireland.

Report prepared by:

Member Company/Institution

Robert Brennan B9 Organic Energy

Stephen Gilkinson Agri Food and Bio-Sciences Institute ( AFBI)

Thomas Cromie AgriAD

Percy Foster Cré- Composting and Anaerobic Digestion Association of Ireland

Beatrice Smyth Queen’s University Belfast

Angela Orozco Questor Centre

Elaine Groom Questor Centre

Simon Murray Questor Centre

Julie-Anne Hanna Questor Centre

Mark Kelly MK Environmental

Morgan Burke Stream Bioenergy

Aaron Black South West College

Christine Irvine South West College

February 2014

Biogas Action Plan for Northern Ireland Feedstock Group coordinated by The Questor Centre

Project partly funded by Invest NI


Appendix 3.1: Quantification of Feedstocks for Anaerobic Digestion

Group Report

Contents

Appendix 3.1: Quantification of Feedstocks for Anaerobic Digestion Group Report ............................. 3

List of Tables ....................................................................................................................................... 3

List of Figures ...................................................................................................................................... 3

Introduction ........................................................................................................................................ 6

1. Organic Resources for Anaerobic Digestion ............................................................................... 7

1.1. Biodegradable Municipal Wastes ........................................................................................... 8

1.1.1 Municipal and Commercial & Industrial Organic Waste Arisings ................................. 10

1.2. Manures ................................................................................................................................ 13

1.3. Agricultural crops .................................................................................................................. 15

2. Biogas and Energy Potential ..................................................................................................... 16

3. Reduction of Greenhouse gases ............................................................................................... 21

4. Nutrient Recovery ..................................................................................................................... 21

5. Conclusions ................................................................................................................................... 22

6. References .................................................................................................................................... 23

List of Tables

Table 1. NI Organic/ Biowaste Arisings ................................................................................................. 12

Table 2. Manure produced in N Ireland from housed livestock ........................................................... 14

Table 3. Biogas Potential of different materials (theoretical estimates) .............................................. 17

Table 4. Potential Biogas, Biomethane and Energy Production from waste and grass silage in N

Ireland ................................................................................................................................................... 19

Table 5. N Ireland AD plants in operation during 2013 ........................................................................ 20

Table 6. Potential Reduction of Greenhouse gases emissions by biogas production .......................... 21

List of Figures

Figure 1. Hierarchy of feedstocks and energy potential ......................................................................... 7

Figure 2. Classification of feedstocks potentially available for AD in N Ireland ..................................... 8

Figure 3. Manure volume from household livestock in N Ireland (as % of total manure) ................... 14

Figure 4. Biogas Energy Potential by Source ......................................................................................... 18

Figure 5. Sensitivity analysis of the average potential gross energy that could be produced from AD in

N Ireland ................................................................................................................................................ 19


Abbreviations

AD Anaerobic Digestion

AFBI Agri-Food and Bio-Sciences Institute

BLACMW Biodegradable Local Authority Collected Municipal Waste

C&I Commercial & industrial

CH4 Methane

CHP Combined heat and power

CO2 Carbon dioxide

DARD Department of Agriculture and Rural Development

DEFRA Department for Environment Food & Rural Affairs

DETI Enterprise Trade and Investment

DoE Department of Environment

EU European Union

G Giga (109)

GHG Greenhouse gas

ha Hectare

Invest NI Invest Northern Ireland

IVC In-vessel aerobic composting

k Kilo (103)

K Potassium

kg Kilograms

kgCO2eq Kilograms of carbon dioxide equivalent

kt kilotonne

kWh Kilowatt-hour

kWhe Kilowatt-hour (energy in form of electricity produced by CHP)

LACMW Local Authority Collected Municipal Waste

m Millions

m³ Cubic meters

MBT Mechanical Biological Treatment

Mha Mega hectares

mt Million tonnes

MW Megawatts

MWhe Megawatt hour (energy in form of electricity produced by CHP)

MWhh Megawatt hour (energy in form of heat produced by CHP)

N Nitrogen

N Ireland Northern Ireland

N/A Not available

N2O Nitrous oxide

NAP Nitrates Action Programme

NI Northern Ireland

NILAS Northern Ireland Landfill Allowance Scheme

Nm3 Cubic meters at normal conditions (0 °C and 1 atm)

OFMSW Organic fraction of municipal solid waste


P Phosphorous

RIA Regulatory Impact Assessment

ROI Republic of Ireland

rWFD Revised Waste Framework Directive

SEPA Environment Protection Agency’s

t Tonne

TJ Terajoules (1012)

tpa Tonnes per annum

TS Total solids

TWh Terawatts-hour

UK United Kingdom

VS Volatile solids

WFD Waste Framework Directive

yr Year


Introduction

Biological treatment options exist for the recovery of organic biodegradable wastes, namely

anaerobic digestion and composting.

Anaerobic digestion (AD) involves the breakdown of organic materials by micro-organisms under

controlled conditions in the absence of oxygen. The products of AD are biogas and digestate. Biogas

typically consists of 55-70% CH4 (but this can be higher), 45-30% CO2 and some minor constituents,

such as hydrogen sulphide (H2S) and water. Methane energy in the biogas can be combusted as fuel

and is commonly used for heat and/or electricity generation. Digestate, which consists of a

suspended solids and a liquid fraction containing soluble nutrients, is the material that remains at

the end of the AD process. Digestate can be used as an organic fertiliser and is reported to be more

suitable than raw agricultural wastes (e.g. slurry, manure) for fertiliser use 1.

Composting is the aerobic decomposition of organic material by micro- and macro-organisms (such

as bacteria, fungi, beetles and worms) in a controlled environment. In N Ireland, green waste only

composting is principally via the open air windrow composting (OAW) treatment method and mixed

wastes (green and food) treated via the in-vessel composting (IVC) methods, required to safely treat

meat and other animal products present in kitchen and oter similar waste. The product of

composting is compost, a nutrient rich fertiliser and/or a soil conditioner.

While both AD and composting provide waste treatment and recovery options, AD is often seen as

the more sustainable of the two practices, largely due to energy, greenhouse gas and aconomic

benefits:

AD is energy positive due to the production of biogas, while IVC requires energy addition.

The electricity difference has been quantified as 125 - 235 kWh/tonne of waste treated, in

favour of AD over IVC 2.

An analysis of the relative benefits of organic waste treatment via AD and IVC by Murphy &

Power 3 (2006) found that AD is more beneficial in terms of green house gas (GHG)

reduction. Anaerobic digestion with biomethane production has the potential to save circa

1,451 kgCO2eq t-1 of bio-waste treated as opposed to IVC, which has the potential to save

circa 1,190 kgCO2eq t-1, 4. As well as reducing GHG emissions, AD is a proven waste treatment

option that reduces pollution from poor waste management practices 5.

AD can also have economic benefits over composting, particularly for larger installations 4.

While the exact figures depend heavily on the tariffs and gate fees in the jurisdiction being

investigated, (In the Republic of Ireland, (ROI) , AD is economically preferable over IVC at

scales above 50,000 t per year of biowaste treated 4.

In summary, the benefits of AD can include 2:

Recycling nutrients and organic matter (digestate) back to land and reducing the

consumption ofchemical fertilisers;

Reduction of greenhouse gas emissions;

Diverting biodegradable municipal waste away from landfill;

Generation of renewable energy;

Creation of jobs in the supply chain;


Heat capture and use in heating schemes e.g. commercial operations and district heating

schemes;

Upgrading biogas (biomethane) to be used as a biofuel for vehices e.g. road freight,

agricultural and similar plant and machinery.

Figure 1 shows the biomass hierarchy potential. The terms of the hierarchy potentials in order of

decreasing size are theoretical, technical, economic, and realistic 6. The scope of this report is to

focus on the theoretical estimates of the organic resources generated and potentially available

within N Ireland only for AD and the biomethane and energy potential generated from these

resources.

Figure 1. Hierarchy of feedstocks and energy potential

1. Organic Resources for Anaerobic Digestion

Organic, biodegradable materials that can be potentially utilised as AD plant feedstocks are listed

below and categorised in Figure 2:

Organic (biodegradable) fraction of municipal solid waste (OFMSW);

Sewage sludge;

Organic industrial and commercial wastes, i.e. food/beverage/tobacco processing wastes,

slaughterhouse/rendering wastes, dairy wastes;

Manure from livestocks;

Food wastes from households, catering, restaurants, hotels; and

Energy crops.

Theoretical

Econo-mical

Technical

Realistic


Figure 2. Classification of feedstocks potentially available for AD in N Ireland

1.1. Biodegradable Municipal Wastes

In 2013, the Department of Environment for N Ireland (DoE NI)published its revised waste

management strategy ‘Delivering Resource Efficiency, Northern Ireland Waste Management

Strategy’ 7 which took account of, for example, the revised Waste Framework Directive (rWFD) -

which placed a much greater emphasis on the implementation of the waste hierarchy) and the UK

Climate Change Act 8 (CCA- which places a duty on the UK to ensures that its net carbon account for

all six Kyoto greenhouse gases for the year 2050, is at least 80% lower than the 1990 baseline.

Organic Resources

Agriculture

Crops

- Grass Silage

- Sugar Beet

Residues

- Wheat straw

Manures

- Cattle

- Pig

- Poultry

Municipal

- Household

- Canteen

- Sewage Sludge

Commercial and Industrial

- Fruit and vegetables

- Industrial

- Supermarkets

- Tanneries

- Food processors

- Catering

- Dairy

- Fish processing

- Slaughter houses

- Food Scraps

http://en.wikipedia.org/wiki/Kyoto_Protocol

http://en.wikipedia.org/wiki/Greenhouse_gases


As with the rWFD, the Strategy’s emphasis is on resource efficiency as opposed to resource

management, i.e. the use of resources in the most effective way while minimising the impact of their

use on the environment. The Strategy was also prepared on a number of other premises including;

sustainable development, climate change, the green economy and health and social well-being and

encouragement of a holistic approach for the development of solutions that encompass all waste

including the broader definition of municipal waste and exploring opportunities for integration of

waste streams.

The 2013 Strategy sets out the following targets:

Achieve a recycling rate of 50% (including preparing for re-use) of household waste by 2020.

Achieve a recycling rate of 45% (including preparing for re-use) of household waste by 2015.

Achieve a recycling rate of 60% (including preparing for re-use) of Local Authority Collected

Municipal Waste (LACMW*) by 2020.

*In agreement with the European Commission the definition of municipal waste in Northern

Ireland has been broadened and this is reflected in the revised Strategy. Previously, the definition

of municipal waste only included wastes which were collected by Councils however, the definition

now includes waste from all households and all wastes of a similar nature and composition to

households, including commercial wastes, whoever collects it. These wastes are now defined as

Local Authority Collected Municipal Waste (LACMW) and the biodegradable fraction referred to

as Biodegradable Local Authority Collected Municipal Waste (BLACMW).

The revised strategy also introduced a Voluntary Agreement Target (involving many of the leading

companies from the UK Hospitality and Food sector) which is to:

‘Achieve a reduction in food and associated packaging waste by 5 %

and to increase the overall rate of such waste which is recycled,

sent to AD or composted to 70 % by 2015’ 7.

In the revised strategy, the DoE NI expressed its commitment to promoting separate food waste only

collections - If collected this way such waste is potentially ideal as an AD feedstock having lower

levels of ‘contamination’ compared to co-mingled mingled (green and food waste and organic

fractions in residual waste stream collections) and if ‘contamination’ such as food packaging does

not result in the digestate failing to meet end of waste criteria. The DoE NI is also committed to

working with the Department of Agriculture and Rural Development (DARD) to look at issues relating

to agricultural waste infrastructure, and also with NI Water in relation to the disposal of sewage

sludge, - one aim being to identify opportunities to utilise feedstock from the municipal waste

streams in AD or IVC facilities 9.

Through the Strategy, the DoE NI also lends its support to innovation and the encouragement and

appropriate use of new treatment technologies, where such technologies can provide the flexibility

required to adapt to changing feedstock over time - that is, being able to adapt to recover the best

value from residual waste while delivering the best environmental outcomes.

Given the proposed introduction of a ban on the landfilling of separately collected food waste (see

1.1.1. below), there is significant scope and potential existing treatment technologies including AD

and IVC, to accommodate future changes in the management of (bio) waste arisings.


1.1.1 Municipal and Commercial & Industrial Organic Waste Arisings

In this and in subsequent sections, waste arising data that were obtained from a number of

referenced publications are presented. It is acknowledged that the data and the Biogas Action Plan’s

use of this data will not be without limitations due to the methods used to collect, analyse, interpret

and extrapolate the original data and the assumptions and uncertainties that are inherent within

them. In preparing the Biogas Action Plan it is acknowledged that the data and their sources are

treated as technical references, as the starting point to inform the development of the Plan and to

stimulate further debate and research.

Across the period 2002 to 2013, reported municipal waste recycling and composting rates in

N Ireland increased from approximately 9% to approximately 45%. The ‘Northern Ireland Local

Authority Collected Municipal Waste Management Statistics Annual Report 2012-2013’ 10 reported

that:

The total LACMW arisings were 913,546 t. Of this amount, 91,216 t of municipal compostable waste

excluding all wood, was collected at the kerbside and 59,555 t collected at Civic Amenity sites

(150,772 t total) with 142,798 t (or 15.6%), reported as being composted.

The total household waste arisings were 803,624 t, with 141,428t (or 17.6%, excluding all

wood) reported as being composted.

The estimated available compostable material, as household kerbside collected waste was

239,418 t. 90,938 t was captured in the 2012-2013 period which is a capture rate of 37.9%,

meaning that 148,480 t or 62.1% of compostable material was not captured in household

kerbside separate collections.

276,702 t of BLACMW was sent to landfill.

The Food Waste Regulations 11 (N Ireland) 2013 (implementation pending) proposes measures to:

Require food waste producers to present food waste for separate collection;

Introduce an obligation on District Councils to provide receptacles for the separate collection

of household food waste;

Introduce a ban on mixing separately collected food waste;

Introduce a ban on the landfilling of separately collected food waste;

Introduce a ban on the non-domestic discharge of food waste into the public sewer network

Changes to existing and/ or additional waste collection services and the establishment of additional-

treatment infrastructure capacity amongst other matters, are likely to be required to facilitate the

implementation of and compliance with the Regulations.

The (partial) Regulatory Impact Assessment (RIA) 11 completed for the above Regulations estimated:

The food waste collected by Councils for the period 2011/ 2012, to be 12,820 t (comprising

12,113 t co-mingled and 707 t from separately collected food waste); and

The (indicative modelled) estimate of food waste that could be diverted from landfill if

councils were to offer a separate food waste or comingled collection service as 79,960 tpa

(comprising 21,119 tpa from co-mingled collections and 58,841 tpa (maximum 59,062 tpa,

minimum 58,619 tpa from separate collections).


From the examination and comparison of other data sources to the RIA’s estimates a number of

observations were made:

The RIA referred to an unreferenced waste compositional analysis carried out for N Ireland

in 2008, which estimated that ‘25.6% of all kerbside collected waste per household is organic

(food) waste, equivalent to 206,000 tpa’. The amount of compostable (food and green/

garden) waste potentially available from household kerbside collections is estimated in the

2012-2013 Northern Ireland Landfill Allowance Scheme (NILAS) Statistics, at 239,418 tpa.

When compared against the RIA’s estimate of 79,960 tpa of household collected food waste,

the 206,000 tpa food waste only arisings would appear high.

The RIA estimated household and C&I food waste arisings of 79,960 tpa and 150,000 tpa

respectively (overall 229,960 tpa) is approximately 10,000 tpa less than the 239,418 tpa of

compostable (food and green waste) stated in the 2012-2013 Statistics Report as being

potentially available. By this measure the amount of compostable non-food waste, that is;

green/ garden waste available in N Ireland, would be 239,418 tpa less 229,960 tpa, or

approximately 10,000 tpa. This figure is much lower than would be expected.

The RIA also provided figures for non-domestic food waste arising in N Ireland. In the lack of

N Ireland- specific data, these were based on the assumption that commercial food waste

composition and arisings in the UK were broadly indicative of that in N Ireland pro rata. The most

reliable figures available to the DoE when preparing the RIA were WRAP’s “Northern Ireland Priority

Materials report” (2012), which suggested (indicatively) that for 2009, of N Ireland’s 1.3 mt C&I

waste arisings, approximately 150,000 t was food waste, managed as follows:

36,443 t (in residual waste) disposed to landfill

34,935 t other

15,441 t reused

61,579 t recycled/ composted

With the proposed ban on the disposal of food waste to sewer from non-domestic sources (the

proposed ban does not apply to households) via Food Waste Disposal Units, the RIA provided

indicative estimates for the amount of commercial (and household, not presented below) food

waste disposed to sewer this way:

Food waste discharged from (non-domestic) commercial FWDs: 8 t/day (or 2,920 tpa).

The waste arisings, treatment data and information in Table 1 are compiled from published sources

of information. For the purpose of this Biogas Action Plan, these figures are considered to best

represent the most likely ranges of Municipa, Commercial and Industrial (organic) Waste arisings

and were susbequently used to estimate the potential biogas (biomethane) and bioenergy

generation potentials which are summarised in Table 3 and Table 4 in this report.


Table 1. NI Organic/ Biowaste Arisings

Waste Quantity (Tonnes/year) Current Management

Data Source OESa WRAP b SWaMP2008 c

Municipal

Household 188,000 381,320 162811 Composting, Landfill

Sewage Sludge (dry) 39,000 37,700 39,000

Incineration

Total 227,000 419,020 201,811

Commercial and Industrial

Retail food 35,700

Composting, pet food, returned to original supplier

Catering 4,140 Composting, Landfill, to drain sewer

Food Processing 26,000 Landfill, animal feed, composting

Slaughter House 178,230

Land spreading, rendering, animal food

Dairy 13,200 Land spreading, animal feed, landfill

Drinks and Distillery 12,000

Animal feed

Animal and vegetables waste 145,573

Landfill, animal feed, composting

Green and Food Waste 189,150

Landfill, animal feed, composting

Total C&I 269,270 189,150 145,573

Total Organic Waste 496,270 608,170 347,384

a Organic Energy Study (2010) 12; b WRAP priority Materials (2012) 13; c SWaMP2008 report (2013) 9

As previously stated , the waste arisings data vary (significantly) from source to source and as

suggested by the reports respective authors should be accepted with caution due to inaccuracies

and uncertainties cing from how the data were collected, reported and used.

The ‘Organic Energy Study Report’ 12, published by Invest NI, reviewed the magnitude and extent of

organic & food waste arisings in N Ireland. The information and data were collected by using a

combination of methods including engagement with a range of public & private sector organisations,

interviews and a survey of all companies of significant magnitude operating in the range of

commercial and industrial sectors within N Ireland .

The WRAP Report, ‘Tackling Priority Materials in Northern Ireland’ 14 gives the highest estimated

value for annual household and commercial and industrial organic waste arisings. The report also


identifies food waste as one of a number of priority materials which was not identified as a priority

material in the N Ireland waste management strategy 2006 – 2020 15 and highlights the benefits of

food waste treatment via AD or IVC.

At the time of writing, according to WRAP, ‘the quantity and rate of uptake of organic/ biowaste

being recycled was very low, with only 13% of food waste being collected through mixed food and

garden waste organic collection schemes for treatment at IVC facilities. Of the relatively small

amount of AD treatment capacity that is presently available in N Ireland, very little of this AD

capacity is assigned to the treatment of these types of biowastes. The WRAP report also states that

N Ireland’s local authorities generally have a low participation in the collection of C&I food waste,

specially outside of urban areas 14.

Tables 2 and 3 in the WRAP 14 report present their suggested interventions which are aimed at

overcoming the barriers identified to tackling household and C&I priority food waste streams, under:

collections, infrastructure, contractual/financial, information, behavioural and waste prevention

headings.

Sewage sludge from NI Water’s Waste Water Treatment Works is currently dewatered and sent to

an incineration plant in Belfast under a public sector contract that runs until 2032 16.

The final report referenced is the ‘SWAMP2008 Waste Management Plan’ 9, which provides its

estimates for the quantities of Municipal and C&I organic/biowaste generated within the south-west

region of N Ireland and within N Ireland as a whole.

1.2. Manures

Agricultural manures were previously excluded from regulations that controlled the management of

household, commercial and industrial waste. The implementation of the Waste Management

Regulations (N Ireland) 2006 (S.R. No. 280 of 2006), as amended, has however resulted in waste

management controls now applying to agricultural manures in accordance with the European Waste

Framework and Landfill Directives 9.

Table 2 shows that approximately 10.8 million tonnes of manure are produced in N Ireland per year.

The manures considered are cattle, pig and poultry. For cattle it was assumed that they are kept

indoors for 6 months. Cattle manure is the main contributor (Figure 3) to the total manure available

in N Ireland. It is important to note that the ‘animal units’ in Table 2 can vary within a year, and

numbers present may not be counted for the full year in the agricultural census. This is especially

true for poultry units, due to the short life span for broiler chickens (about 5 to 8 weeks).

The factors which affect the biogas potential of manure include: collection methods, storage

temperate and length of storage, total solids content (TS), volatile solids content (VS) and the

digester degradation efficiency. The anaerobic digestion of agricultural manures is a sustainable

method of treating this material 17.

Results from work at AFBI indicate that the fertiliser value of digested cattle slurry is increased by

about 15%. Hence digestate has the potential to reduce the need for inorganic (manufactured)

fertilisers, which has both economic and environmental benefits.


Table 2. Manure produced in N Ireland from housed livestock

Animal Sector

Animal Units a

Approximated Manure b

(tonnes/year)

Cattle 1,625,400 10,000,000

Pig 383,700 500,000

Poultry 19,188,200 300,000 c

Total

10,800,000

a Animal units were taken from Agricultural census 2012 18

b Manure quantity was calculated multiplying the animal units by the excreta produced per month 19, values were rounded

c Poultry manure quantity was obtained from industry sources

Figure 3. Manure volume from household livestock in N Ireland (as % of total manure)

Land spreading of animal manures is allowed under strict conditions, in accordance with the Nitrates

Action Programme Regulations (NAP) (Northern Ireland) 2010 and the Nitrates Action Programme

(Amendment) Regulations (Northern Ireland) 2012 (NAP Regulations). Due to the high nutrient

content of chicken manure and its potential to cause botulism in cattle, land spreading is a limited

Cattle 93%

Pig 4%

Poultry 3%


option. The EU Nitrates Directive 91/676/EEC places a limit of 170 kg organic manure

nitrogen/hectare/year that can be applied to agricultural land on any one farm holding. Any farm

that exceeds this limit is required to export manure to other farms that are below the 170 kg limit to

ensure compliance with the regulations. The option to export manure is not always readily available,

as the 170 kg limit restricts the area available for exporting excess manure and therefore, there is an

urgent need for an alternative to land spreading poultry litter.

Traditionally poultry litter has been spread on agricultural land but this practice is not sustainable in

the longer term. AFBI has concluded that land spreading on grassland is not an appropriate disposal

route for poultry litter due to environmental problems and other constraints 9. Poultry litter has

relatively high phosphorus content and its application to land over time may exceed agronomic need

and result in phosphorus surpluses in a significant proportion of local agricultural soils (this has

already happened). Phosphate losses via run-off contribute to nutrient enrichment of streams, rivers

and lakes (eutrophication), which is an important water quality issue in N Ireland.

Action to address nutrient enrichment of waterways is required under both the EU Nitrates Directive

and the EU Water Framework Directive and hence a more sustainable and practical way of managing

poultry litter in N Ireland is urgently needed. In order to address this issue, Invest Northern Ireland

(Invest NI) on behalf of DARD and the Department of Enterprise Trade and Investment (DETI) is

currently running a Small Business Research Initiative Competition (in partnership with the

Technology Strategy Board) to stimulate the development of sustainable and innovative solutions for

the utilisation of poultry litter in N Ireland.

1.3. Agricultural crops

According to analysis by Goulding & Power (2013) 17 biogas produced from grass silage can make a

significant contribution to electrical and thermal energy production in Ireland, with no negative

effect on food production. Most agricultural land in N Ireland is in grass as grass is the main

feedstock of the ruminant livestock sectors – beef, dairy and sheep. An area of 0.78 Mha (excluding

hill and rough land) 18, is utilised for growing grass and clover in N Ireland. Much of the land under

grass is unsuitable for alternative arable use, due to the topography and climatic conditions 20.

Figures collated by DEFRA (personal communication) indicate that the average application rate of

inorganic nitrogen is circa 74 kg/ha/yr. The respective figure for organic nitrogen (N) loading is circa

134 kg/ha/yr.

The Nitrates Directive allows up to 222 kg/ha/yr inorganic fertiliser, plus organic nitrogen up to

170kg/ha/yr. Hence there is scope to increase the amount of grass (silage) produced from the

same/reduced land area, by increasing the amount of inorganic N applied, without displacing land

that is currently used for food production. Results from field trials at AFBI, Hillsborough, indicate

that, at the maximum permissible inorganic fertiliser application rates and allowing for organic N

contribution from applied manures, the resultant production of herbage is in the order of

12 - 14 tonnes dry matter/ha/yr. However, about 15% of this can be lost in the harvesting and

fermentation process.


The electrical output per hectare of land devoted to grass silage production for anaerobic digestion

is dependent on three main parameters; the dry matter yield, the digestibility of the dry matter and

the CHP electrical efficiency and runtime. The electrical output per hectare can range from circa

0.77 kW to 2.5 kW, but is likely to be in the region of 1.6 kW (based on data from AFBI). If 5% of the

grassland area in N Ireland was dedicated to grass silage production for anaerobic digestion (39,000

ha), the electrical output from this would be circa 62 MW (continuous energy output), equivalent to

39% of the average N Ireland electrical demand. There is also heat output that could be used to

offset fossil fuel usage.

The reasons for using grass to produce renewable energy in N Ireland are include:

• 92% of agricultural land in N Ireland is under grass.

• Grass/silage yields in Ireland are among the highest in Western Europe 21.

• The production of renewable energy (as biogas) from grass requires no major changes in

agricultural practice and would provide an additional option to farmers for income

generation.

• Agriculture accounted for 26% of N Ireland’s greenhouse gas emissions in 2010 22. AD is a

method to reduce agriculture’s carbon footprint.

• In 2010, 96% of fuel used in N Ireland was imported and the vast majority of this was from

fossil sources 23. AD has the potential to reduce this dependence on fossil fuel.

• Bio-methane production from grass is one of the most sustainable indigenous, non-

residue based European transport fuels in terms of GHG emissions 24, 25. When used as a

transport fuel, GHG savings greater than the EU target are readily achievable 24.

• The Agri-Food Strategy Board is targeting significant increases in agricultural output from

N Ireland. As well as reducing GHG emissions from this increased production by digesting

agri-food ‘wastes’ and manures, AD could play a vital role by sustainably recovering the

increased waste arisings from this sector.

It is concluded that the generation of renewable energy for use as heat and transport fuels is falling

short of government targets, and there is no clear plan for N Ireland to achieve these targets. The

anaerobic digestion of grass to produce biogas or biomethane is put forward as a multifaceted

solution, which could help meet energy and emissions targets, reduce dependence on imported

energy, and provide additional farm income.

2. Biogas and Energy Potential

Table 3 shows the theoretical estimates of biogas potential of different materials used as feedstocks

for anaerobic digestion.

A typical household in N Ireland consumes on average 3.7 kWh 26 electricity per year, and the

domestic electricity consumption in 2011 was 2,825 GWh 26, therefore it would be theoretically

possible to generate electricity for circa 85% of the households in N Ireland. There are practical

issues with the supply of heat, as it will require significant infrastructure investment. On-farm AD

plants are in most cases likely to be too far away from large scale users of heat to make heat export

economically viable. Figure 4 shows the energy estimates in percentage terms that that can be


potentially generated from the feedstocks identified in this report. If utilised in AD, they could make

a significant contribution to renewable, bio-energy generation. The most significant contributions

are from grass silage and manure at 45% and 42% respectively of the total possible (based on the

figures in Tables 3 &4).

Table 3. Biogas Potential of different materials (theoretical estimates)

Category Total Solids Volatile Solids Methane Yield Methane

Content

(%) (% of TS) (m3

N CH4/tonne

VS) (%)

Household 27 10 80 350 - 480 70 - 80

Sewage Sludge

(2-5 % VS) 28, 29 2 - 5 65 140 - 210 60 a

Retail food 28, 30 31 - 41 48 - 85 200 - 440 60 a

Catering 31 29 95 467 - 529 60 a

Food Processing 32, 27 15 80 276 - 738 60 a

Slaughter House 33 10 77 400 -610 60 a

Dairy 34 7 - 56 80 - 99 455 - 708 60 - 80

Drinks and Distillery 34 5 91 335 - 385 60

Dairy Cattle manure 27 5 - 12 75 - 85 110 - 240 55 - 75

fattening Cattle manure 27 5 - 12 75 - 85 111 - 240 55 - 75

Pig Manure 27 3 - 8 70 - 80 175 - 400 70 - 80

Chicken Manure 27 10 - 30 70 - 80 210 - 480 60 - 80

Grass Silage 35 15-25 90 - 92 341 - 483 60 a

a Assumed 60% methane yield


Figure 4. Biogas Energy Potential by Source

Table 4 shows that the estimates of the potential of electrical and heat production from wastes

streams and grass silage is in the range of 458 - 2020 GWhe (electricity) and 655 – 2885 GWhh

(thermal). It is important to note that these figures are the theoretical maximum potential (as

explained in Figure 1). The figures in Table 4 do not include parasitic demands in the AD process. It is

assumed that the AD process of an installed electrical power of 500 kWe digesting crops only utilises

4% of electricity and 17% of heat 36. The additional electricity requirement for upgrading is assumed

to be 0.2 kWh per Nm3 of biogas. These energy requirements are assumed to be supplied by the AD

process itself. If the biogas is going to be used as a vehicle fuel or injected into the gas grid, this will

require an input of electricity of around 6 % of the energy produced 13.

The Government target set for 2012 was 12% of all electricity consumed in Northern Ireland to be

generated from renewable sources 37. In 2011/12, 1,164,000 MWh of electricity in NI was produced

from renewable sources, equivalent to 14.3% of total electricity consumption in that period, showing

a substantial increase in the amount of electricity produced from renewable sources since 2001/02,

when only 128,000 MWhe (1.5% of total electricity consumed) was generated from renewable

sources 37.

Table 5 lists the AD plants that were in operation in 2013 in N Ireland, the average size was 500 kW

CHP and most of them are located on farms, together producing a potential (operational

performance figures are not available) of 4.3 MWe . DETI 23 has reported that AD has the potential to

contribute between 25 and 75 MWe by 2050, .

Total Municipal 3% Total C&I

4%

Cattle manure 42%

Pig manure 1% Poultry manure

5%

Grass Silage 45%


Table 4. Potential Biogas, Biomethane and Energy Production from waste and grass silage in N Ireland

Feedstock Bio Methane1 Gross Energy2 Electrical Energy 3,4 Heat Energy 3,4

(m3N CH4/y)*millions (TJ/y) (GWhe/y) (GWhh/y)

Organic Waste

Total Municipal 5 - 15 164 - 529 16 - 51 23 – 74

Total C&I 4 - 22 159 - 786 15 - 76 22 – 109

Total Organic Waste 9 - 37 324 - 1,315 31 - 128 45 – 183

Agricultural

Cattle Manure 41 - 261 1,455 - 9,253 142 - 900 202 - 1,286

Pig Manure 2 - 5 68 - 178 7 - 17 9 - 25

Poultry Manure 4 – 35 157 - 1,227 15 - 119 22 - 171

Total Manure 47 – 300 1,680 - 10,658 163 - 1,037 233 - 1,481

Grass Silage 76 - 247 2,706 - 8,785 263 - 855 376 - 1,221

Total Potential 133 - 585 4,709 - 20,758 458 - 2,020 655 - 2,885

The total energy consumption in N Ireland, reported by Cambridge Econometrics (2010) 38 on behalf

of DETI was 51.26 TWh (184,536 TJ), from which biogas has the potential to contribute between

2.5 - 11% of N Ireland’s energy demand, assuming that all the energy generated by the methane

produced is used (Table 4).

Figure 5 shows a sensitivity analysis of the average potential energy produced by AD if 10, 25, 50, 75

and 100% of the estimated feedstock is used in AD.

Figure 5. Sensitivity analysis of the average potential gross energy that could be produced from AD in N Ireland

-

2,000

4,000

6,000

8,000

10,000

12,000

14,000

10 25 50 75 100

Ave

rage

Gro

ss P

ote

nti

al E

ne

rgy

(TJ/

yr)

(%)

Total Organic Waste

Total Manure

Grass Silage

Total Potential


Table 5. N Ireland AD plants in operation during 2013

Site Location Feedstock Commissioned Inputs (tpa) Outputs (kWe) Technology supplier Uses

Ballyrashane Co-op Coleraine

•Dairy Waste •Cattle slurry •Grass Silage •Maize Silage

Sep-12 18,800 1,000 Weltec Biopower GmbH CHP

AFBI-Hillsborough Hillsborough •Cattle Slurry •Energy Crops

2008 7,000 23 BiogenGreenfinch CHP

BH (Blakiston Houston) Energy Belfast

•Cattle slurry •Grass silage •Small amounts of whole-crop wheat and Maize silage

Apr-11 12,500 250 Biogas Hochreiter CHP

Hunniford Energy Portadown •Cattle Slurry •Grass Silage •Poultry Litter

2013 35,000 500 Moore Biosystems CHP

JMW Farms Ltd. Armagh •Cattle Slurry •Energy Crops

Jul-05 36,000 500 Moore Biosystems CHP

Holly Park Energy Tyrone •Grass Silage •Cattle Slurry

2012 16,875 500 Hochreiter CHP

Greenville Energy Ardstraw •Slurry •Grass Silage

Aug-12 25,000 500 Williams Industrial Services CHP

GreenFarm Energy UK Ltd. Omagh •Cattle Slurry Oct-08 4,000 40 N/A CHP

IB Energy West Tyrone •Grass Silage •Cattle Slurry

2013 15,000 500 Hochreiter CHP

Frankie Donnelly Ardboe •Cattle Slurry •Grass silage •Food Waste

May-13 15,000 500 AgriKomp CHP

Total

4,313


3. Reduction of Greenhouse gases

The treatment of biowastes via AD is reported to achieve reductions in carbon dioxide emissions

with total CO2 reductions estimated at 173 kg CO2/t waste treated. As AD produces biogas (which

can be used, as a fossil fuel replacement), AD could contribute to reduced CO2 emissions, with

estimated reductions (compared to the use of fossil fuels) of up to 2.5 million tonnes per year of

CO2, equivalent to a reduction in 15% of CO2 emissions when compared with the total emissions in

2010 (14,657 kt 37).

Table 6. Potential Reduction of Greenhouse gases emissions by biogas production

Feedstock Quantity Biogas Production Average

CO2 reduction with CHP production - optimal usea

CH4 and N2O as CO2eq

Total reduction as CO2eq

(t/yr) (m3/yr)*million (t CO2/yr) (t CO2/yr) (t CO2/yr)

Total Organic Wastes 421,827 23 76,927 140,609 b

Total Manure 10,800,000 174 579,223 468,000 c

Grass Silage 1,901,250 162 539,475 633,750 b

Total 13,791,995 359 1,195,626 1,242,359 2,437,985

a CO2 reduction due to displacement of fossil fuels: 2 kg CO2/m3 biogas 39

b Reduction in emissions of CH4 and N2O: estimated 200 kg CO2eq/t, or 2 kg CO2/m3 biogas 39.

c Reduced emissions of CH4 and N2O: approx. 26 kg CO2eq/t, or 1.2 kg CO2/m3 biogas. With improvements to housing and biogas technology, emissions particularly from animal manure can be further reduced 39.

4. Nutrient Recovery

Digestate contains the plant nutrients present in the original feedstock and as a consequence has

considerable value as an organic fertiliser. Typical nutrient values for digestate are given below,

however the actual nutrient content is highly dependent on the type of feedstock processed 40.

Nitrogen (N): 2.3 - 4.2 kg/t.

Phosphorous (P): 0.2 - 1.5 kg/t.

Potassium (K): 1.3 - 5.2 kg/t.

Consideration must be given to the relationship between the quality of the feedstock and the quality

of the digestate as depending on the source and quality, if feedstock is not pre-treated, the resultant

digestate will contain all material, including contaminants that have not biodegraded 40.

AFBI 32 reported that raw slurry and digestate are rich in plant nutrients (N, P and K) and should be

applied to agricultural land in accordance with crop requirements for plant nutrients. Nutrient


management is important for sustainable agriculture and matching nutrient application to crop

requirements is imperative. It is the quantity of plant nutrients applied, rather than volume of

manure (or digestate) applied, that is important.

In England, Wales and N Ireland, digestate produced from certain source segregated biodegradable

wastes that are composted must be certified under the Compost Quality Protocol (QP) and the BSI

PAS 110 specification 41 to meet end of waste criteria. Digestate from AD plants utilising only

manures and/or agricultural crops is not considered a waste, and can be landspread under the same

regulations that apply to undigested manures 41.

In Scotland, the Quality Protocol requirements do not apply, although compliance with BSI PAS 110

is necessary and digestate users must apply digestate in accordance with the Scottish Environment

Protection Agency’s (SEPA’s) position statement on the ‘Classification of outputs from anaerobic

digestion processes’. Digestate certified under the scheme must be used in accordance with good

practice and regulatory controls, particularly where the Animal By-Products Regulations apply.

Digestate not certified under the Biofertiliser Certification Scheme is likely to be still classified as

waste and its use must comply with waste regulations 42.

In 2010, N Ireland imported 360,000 tonnes of synthetic fertiliser at a cost of £80 million. Using

digestate as a local and natural substitute for the synthetic imports could prove advantageous from

environmental and economic perspectives.

5. Conclusions

In N Ireland there is a huge potential to utilise AD as a method for the sustainable treatment

of organic wastes and production of renewable energy, heat and fuel

Waste arisings and compositional data data used to estimate biogas generation yields need

to be interrogated and further refined.

Certain short to medium term arrangements and commitments currently in place for the

collection and treatment of municipal and C&I biowastes and sewage sludge exclude (a

significant amount) of these materials for use as AD feedstocks. To help contribute to

meeting the various regulatory environmental, waste, energy and climate change etc.

targets and objectives and create direct and indirect economic and social benefits, these

arrangements would need to be re-evaluated going forward. Agricultural residues, manures

and grass silage can be used as AD with little impact on current agricultural production.

AD can contribute between 2.5 – 11 % of the total energy demand in N Ireland, adding the

benefits of contributing to reduction of CO2 emissions and the use of the digestate as a

fertiliser, with the possibility of exporting it, due to the content of phosphorous, replacing

the need of using inorganic fertiliser.


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